1. Field of the Invention
The present invention relates to an X-ray CT (computed tomography) device and a myocardial perfusion image generating system for taking contrast CT images such as coronary arterial contrast CT images, myocardial contrast CT images, and so forth, by continuously injecting a contrast medium, and generating a myocardial perfusion image using the obtained contrast CT images.
2. Description of the Related Art
With a myocardial contrast examination using an X-ray CT apparatus, a contrast medium is injected into a subject that is a patient, and contrast CT images are collected. Subsequently, moving images of coronary arteries, endocardial lumen wall, and so forth, are generated from the collected contrast CT images, and are employed for diagnosis.
Also, a blood flow dynamic state (perfusion) examination of the myocardium and a perfusion examination regarding organs such as within a brain tissue have been performed using an X-ray CT apparatus. With these perfusion examinations, attempting to generate a perfusion image by analyzing dynamic contrast CT data obtained from dynamic imaging by bolus injection for injecting a contrast medium in a short period has been conventionally studied.
However, normally, such perfusion imaging is not an isolated examination, but performed as part of a contrast examination. For example, in the event of a myocardial perfusion image, scanning for heart function analysis such as coronary arteries and endocardial lumen movement is also performed as well as scanning of a myocardial perfusion image. Accordingly, it takes a long time for scanning of a myocardial perfusion image, and a examination method resulting in increase of X-ray dosages for the subject ray is hardly acceptable, and accordingly, long-period dynamic imaging using an X-ray CT apparatus has never come into practical use so far. With a perfusion examination regarding capillaries within a brain tissue in light of such a background, a contrast medium is injected into a subject at a time, and images are taken in a short period (see Japanese Unexamined Patent Application Publication No. 2003-116843, for example). More specifically, the contrast medium is injected using a technique such that a temporal peak is formed in the concentration variation of the contrast medium to be inserted into a subject, and imaging with an X-ray CT apparatus is performed synchronously with the timing at which the contrast medium moves to a capillary within a brain tissue. Subsequently, information regarding perfusion is obtained using CT images obtained by imaging using the X-ray CT apparatus based on the temporal concentration variation of the contrast medium in the capillary within the brain tissue.
However, with a conventional technique for obtaining information regarding perfusion by injecting the contrast medium into a subject at a time, the X-raying period of the subject can be suppressed as well as the amount of time for imaging, but additional X-ray imaging is necessary for collecting data for organs other than perfusion, such as coronary artery images and heart function analysis data. Accordingly, further reduction in the shooting period is required.
Furthermore, the number of times of contrast-medium injection and the amount of injection increase as the imaging time increases, since scanning is performed for taking of myocardial perfusion images and myocardial images, respectively. However, the amount of injection of the contrast medium as to a subject has an upper limit, and consequently, the amount of time for imaging and the number of times thereof are also restricted. Accordingly, this presents a problem in that it is difficult to secure long imaging time for myocardial perfusion images.